There is no question that Oxygen Toxicity effects exist - even at less than 100% Oxygen - if the pressure is high enough to make PO2 more than about 500 mmHg. For extended periods 760 mmHg PO2 (even subtracting 40 mm PCo2 and 47 mm PH2O) is definitely dangerous with regard to Oxygen toxicity. This particular effect is uniformly identified with the partial pressures listed, and not associated with the presence or absence of buffer gasses.

I have been begging for input (see HELP WANTED) on a number of subjects. I know that there are people who understand these problems better than I do. I DO NOT, HOWEVER, BELIEVE THAT THE BEST ANSWERS WERE FOUND LAST CENTURY!

I certainly welcome the “Doc’s” input on these physiological problems: (Dr_Keith_H)
“Well spotted. Lung damage can occur with prolonged exposure to 50-100% Oxygen.
100% Oxygen can cause damage and onset of oedema in about 24 hours, at normal atmospheric pressure.

Please forward any references you have on this matter. While I have your attention, can you supply any information on Pulmonary Barotrauma? I do mean with healthy lungs, as emphysema and related COPD do increase damage sensitivity. Therapeutic positive pressure ventilation seems to be limited to 60 cm H2O pressure (44 mmHg), which, if sustained, is described as “making exhalation very difficult”. With elastic chest banding (or the pressurized vest portion of a “G” suit) this difficulty is reduced. I would really like to know what pressure level is used for the positive pressure breathing in the F-22 “partial Pressure Suit”, as this has been chamber tested at 20km equivalent altitude – quite near vacuum.

What I remember is that breathing pure Oxygen was neither a problem nor a concern for Apollo. And I agree, that the benefit of adding Nitrogen as a buffer gas is not at all clear (adding water with humidifiers is of course common in Oxygen breathing systems). It is not enough that problems were suspected, and that using normal air was a safe answer. Aerodynamic heating is also a known problem. - but the use of welded titanium as a “preventative solution” was rejected by Burt Rutan. We may need to think again about many parts of our space systems before they become affordable!

The big, gas mixture change followed the Apollo 1 capsule fire. That was assumed to show that pure Oxygen has an excessive fire danger. I have it on good authority that the fire danger in Oxygen at reduced pressure quickly falls below that in normal air.

What the Apollo capsule fire showed is that two atmospheres pressure of pure Oxygen, with PVC wire insulation, a defective and poorly fused electrical system (intermittent communications from the beginning of the test) and no safety systems, is a bad idea. In fact, the test, with exactly these conditions, was not treated as a hazardous operation. If the capsule had been fitted with a CO2 “flood”, extinguisher system (and a pressure relief rupture disk), those astronauts might still be alive today. (I have seen powerful CO2 extinguisher systems built into dragsters). This catastrophe would have been prevented by forethought about any of the listed elements. Only in the political climate would the response be to add multiple complex “solutions” to “fix” a trivial problem.

And yes, the same logic applies to: “don’t launch in subzero weather – it reduces “O” ring effectiveness, and these are already marginal”, and “Don’t ignore stuff flaking off and hitting the wings during launch – the leading edge is critical at reentry, yet is brittle and could be damaged.” A healthy organization doesn’t trivialize problems until they create a very public disaster, and then overreact in a great flap. Yet, I am not sure that a government funded organization can be “healthy” in normal terms.

My Russian Spacesuit book has a great many details, including listing more than 200 EVA operations, but does not address why the complexity of mixed gas is added to the space station. As a side note, this 20 + year experience, and the long MIR operation, explains why the Russians supplied the breathing system for the ISS. A corollary of this is the fact that NASA has never seriously addressed life support systems for efficient long duration spaceflight! If they had, a NASA life support system would certainly have been used on ISS. Thus NASA accomplishments and future assumptions in this particular area mean very little, and should not be used as a planning baseline: they never really tried!

It is not that NASA is better at space work than others – it is just that when you throw billions of dollars at a problem, most of the world’s experts are willing to come and work temporarily in the USA. In fact, NASA efforts have been pragmatic rather than visionary, adapting military aircraft technology whenever possible. And the military has never needed EVA systems, or multi-day life support. In point of fact, the ISS EVA suits have demonstrated a reliability that would be unacceptable for even recreational diving gear, let alone serious professional equipment.

The first computer I had access to, in 1961, was the IBM 7090. I understand that this machine (or possibly its vacuum tube predecessor, the IBM 709) had a mean time to failure of 3 days. It required one or two technicians on staff to keep a computer facility up and running. Its computing power didn’t compare to a pocket “Game Boy”. How many computers could you sell today with a 3 day mean time to failure? The entrepreneurial community (with me as a part of it) will produce high reliability systems when someone wants them.

Regarding the “zero G compatibility” of my system: Of course I will have an emergency backup system when I personally demonstrate it in orbit. (My Fish named Wanda, on the other hand, will have to do without the backup system). When will either test become possible? God only knows! That is the biggest problem with space access development; Nobody can afford to do the tests to develop the hardware to make such testing affordable. That is why I have been pleading, in a number of forums, for a general commitment to replace ORBITAL BALLAST (which is usually carried with a launch) with space experiments. And, at the same time, I have been working to make an orbital demonstration as light as possible, equaling a small portion of orbital ballast. If anyone knows of a launch vendor willing to make such a commitment, (with affordable “engineering costs”) let me know.

Of course “faith” is exercised regularly in engineering, and many things are done which differ significantly from their predecessors. Surprises happen when the model used to validate the design misses a significant factor. This is actually more likely today, since computers give the image of power and sophistication, while hiding the fact that the real world is too complex to simulate and the programmer has limited information. Why did it take so long to realize that a “puffy piece of foam”, traveling at several hundred miles a hour, could damage a brittle RCC wing leading edge?

The problems of “zero G” I spelled out earlier: No convection currents. + unpredictable liquid/gas interfaces relevant both to dissolved gasses in liquid, and vapors in a gas. (The lack of convection can also create a heat transfer problem). These are clearly definable by physical principle. (If I missed anything here, let me know). These I am addressing in more detail than my reports will capture.

Does this miss something important? That was the question when “Ham” flew into space. “Was there something else about spaceflight, and lack of gravity, that would kill the passenger/pilot?” Ham came back alive, and answered the question. In point of fact, the human organism – somewhat like the work of a good designer (?) – does a very good job of controlling the dissolved gasses, and free vapors in its internal systems, and provides quite adequate pumps. It is not very position sensitive, and operates nicely in “zero G”. A similar engineering approach has a high likelihood of succeeding.

Apollo 1 used high pressure 100% oxygen for the leak check on the pad. This was clearly a bad idea. After the fire it was changed to air for the leak check, but after launch the cabin was purged with pure oxygen while being vented down to the 3 psi (or so) flight pressure. I had always assumed that pure oxygen at the same pressure as the partial pressure of oxygen at sea level would be safe, but all the references imply otherwise. I have not found any information specifically stating what the health problems are at low pressure are though. I really hope they didn't use mixed gas on the shuttle and ISS for no good reason! Or if they did, I hope we can fix that.

Tests revealed that a 60-percent-oxygen and 40-percent-nitrogen mixture at a pressure of 11.2 newtons per square centimeter (16.2 pounds per square inch) on the pad would result in 1.4 newtons (2 psi) in orbit after venting, which would give a partial pressure of oxygen compatible with the oxygen atmosphere and pressure in the suits. The cabin pressure would be lower at first, but the mixture would be breathable and it would sustain life. In fact, by the time the craft reached orbit, Faget said, the cabin mixture would actually be about 80 percent oxygen. And there was a bonus in this arrangement beyond the safety factor: no structural changes were needed in the spacecraft to accommodate this combination of oxygen and nitrogen.

Low promised Phillips a decision on the prelaunch atmosphere in time for spacecraft 101's Design Certification Review. A third set of tests, using boilerplate 1224, confirmed conclusions drawn from the second series. Gilruth's Flammability Board met on 4 March and recommended the 60/40 mixture for the launch pad. On 7 March, Mueller's Certification Board accepted this recommendation. In April, NASA's medical group, expressed "enthusiastic approval of the . . . decision to adopt the 60/40 atmosphere."

(ANOTHER EDIT) And more googling.
http://msis.jsc.nasa.gov/sections/section05.htmsays, "Prolonged breathing of pure oxygen at sea level pressure (and perhaps even at lower pressures) can eventually produce inflammation of the lungs, respiratory disturbances, various heart symptoms, blindness, and loss of consciousness."
My emphasis on "perhaps".
It sounds to me like NASA is just ASUMING there COULD be problems without knowing. I see an opportunity here. Volunteers could spend extended periods in chambers with low pressure pure oxygen atmospheres while undergoing medical monitoring.

However, later in the same document it says this, "For long durations (in excess of two weeks) some physiologically inert gas must be provided to prevent atelactasis." So maybe tests have been done already.

By the way, another page I found said the shuttle looses 9 pounds of nitrogen and 7.7 pounds of oxygen per day to leakage. I also know that SS1 cabin pressure is regulated by constantly admitting oxygen from a bottle to balance the cabin leak rate. Any long duration flight will need MUCH lower leak rates.

Could another potential problem with prolonged exposure to pure oxygen be a dearth of nitrogen intake? Nitrogen is one of the elements essential to all life; I would think that going from breathing 11 psi worth of nitrogen to none at all would have some detremential effects. I'm not really that knowledgable about biology, but for some reason the idea of not breathing any nitrogen for long timeframes raises a little red flag in my mind.

If there is no problem with not breathing nitrogen but a serious one with pure oxygen, why not use an inert gas as a buffer? Helium and neon would take up much less mass than nitrogen to supply the same equivalent pressure, and would be very helpful in keeping the cabin from going the way of Apollo 1. Boiloff might be a serious problem though, I could see that as being a potential kink in this system. I don't see it as being very likely that NASA used an O2/N2 gas system for no good reason, so that's probably the best way to go for long duration operations, but it would be nice to know why exactly.

_________________"Yes, that series of words I just said made perfect sense!"
-Professor Hubert Farnsworth

Note on biology, the human has no "Nitrogen Fixing" mechanism, and must supply ALL its nitrogen needs from food (protein)

I agree with your emphasis on the word “Perhaps”

says, "Prolonged breathing of pure oxygen at sea level pressure (and perhaps even at lower pressures) can eventually produce inflammation of the lungs, respiratory disturbances, various heart symptoms, blindness, and loss of consciousness."
My emphasis on "perhaps".

Oxygen toxicity is well known, but depends on the partial pressure of Oxygen, not the percentage in a mixture.

About atelactasis;
Definition: Collapse of pulmonary alveoli lacking ventilation while their blood circulation continues to function.

Bohm SH, Bangert K. says this in his paper (found Googling atelactasis):
“During general anaesthesia even healthy lungs tend to collapse. Thus, up to 20% of previously functional lung tissue may be lost for gas exchange.”

Thus this is a not something extraordinary, but a common occurrence (and happens during an hour or two of surgery, and not in days). It is usually dealt with by encouraging a patient to breath deeply. Sometimes using an accordion like device to breath into, to demonstrate the effectiveness of these respiratory efforts (particularly when abdominal surgery makes these efforts somewhat painful, and encourages the patient to use shallow breaths). It is likely that positive pressure ventilation will cure this problem, and I expect such systems to be onboard for EVA and emergency use. It is possible that dry gases, as used in aircraft Oxygen systems, are part of the problem. It is also likely that if this possibly minor effect is troublesome, or progressive, that a Nebulizer for inhalation therapy could be used.

It looks a whole lot like an obscure medical word is being used to describe a minor medical condition, to help justify the politically motivated decision to change the gas mixture from what was used in the Apollo fire, to “normal air”.

Your idea of doing low pressure chamber tests is excellent, although a bit complicated. It would be less complicated in a trailer atop Pikes Peak, where the total air pressure is less than 60% of sea level (avoiding Oxygen toxicity). Yet since this effort could cut the cost of a Mars mission by up to 50%, it is well worth doing – if we ever intend to walk on Mars (and live on Mars – hopefully not in “Earth Normal Domes” – which make it very difficult to go outside).

One basic note: lower total gas pressure does increase the diffusion rate. Normally this is good in the lungs. But with DRY gas it may cause excessive drying of part of the airway structure which are not normally subject to such rapid water loss. These effects may be related to the “climbers cough” experienced by many high altitude mountaineers. This is not objectively a serious problem, as they still achieve prodigious feats, climbing into the stratosphere. In fact, select individuals have achieved physical ability – WITHOUT ADDED OXYGEN – at the pressures we are talking about (less than 4 pounds per square inch atop Mount Everest).

KEEP UP THE GOOD WORK! We are closing on what is actually "known" about these space flight problems, and what has been assumed.

Perhaps 3 psi is just too low a total pressure. Even though pure oxygen would be at the same pressure as it's partial pressure at sea level, maybe human lungs need some minimum level of total pressure to stay fully inflated. What I am trying to say is that maybe it is a low total pressure problem and not an oxygen problem. After all, damge to your body by a vacuum is due to lack of pressure and not due to lack of oxygen (at least in the first few seconds).

Last edited by campbelp2002 on Sun Apr 10, 2005 3:22 pm, edited 2 times in total.

I recommend you guys go read the copious relevant materials available in the journal called Aviation, Space and Environmental Medicine rather than asking internet jocks for information. Through that journal rpspeck should be able to directly contact the researchers who truly know the answers to his questions.

On another note, Google is like the ultimate "yes man" ... it will usually tell you what you want to know, even if it is not true. So treat the internet as a very dubious source for accurate information.

All right, so zero nitrogen is not a potential problem. Even if pure oxygen is okay from a biological standpoint it's probably too risky to use for prolonged missions considering that practically anything that can burn will do so in a pure O2 environment if given the proper impetus (as in a single spark). It's no fun for anyone if the crew cabin goes kablooie halfway to Mars.

How about setting up the LSS for 6 psi of pressure, half oxygen and half neon? That way reduced pressure effects are mitigated if not removed entirely and the cabin environment is less eager to turn itself into a white-hot blowtorch. IIRC the Air Force's MOL project was going to use an oxygen/helium environment before it was cancelled, which seems to indicate that oxygen/noble gas systems can work. I'm not sure the crew could stand breathing helium for two years on end, though. Neon is lighter than nitrogen, and less suseptible to leakage than helium, so it appears to be a nice compromise. Please do NOT take my word for it, however, as I'm afraid I don't have any professional experience in any of the fields we're talking about. Intellectual curiosity, yes, but I encourage you to find real, legitimate sources before doing any real work.

_________________"Yes, that series of words I just said made perfect sense!"
-Professor Hubert Farnsworth

Pure O2 at 3 psi is as safe as 21% O2 at 14 psi. The Apollo 1 fire occurred because they used 100% O2 at 18 psi on the pad for leak checking. Any idiot should have known that was dangerous. In fact the company that built the Apollo CM (North American, now Rockwell) did say it was dangerous, but NASA disagreed! In flight it would have dropped to 3 psi, which is perfectly safe, which is what all other Apollos did. The only difference is they used a 60/40 mix of O2 and N2 for the leak check on the pad.

The reason to use pure O2 is reduced complexity due to only one tank of O2 instead of one for O2 and another for N2, but also no need to control the ratio. (How do you know if your 14 psi is 50/50, 100% O2 or 100% N2? Simple, 100% N2 kills the crew! This was one of the reasons NASA didn't want a mixed atmosphere.) Also, a 100% O2 craft can operate at 3 psi. A pressure vessel capable of holding 14 psi is much heavier than one that only has to hold 3 psi.

Copius is right! I am having trouble finding anything in all that! I tried searching the abstracts for information about low pressure 100% oxygen atmospheres, with no luck so far. For example, no abstract has both the words "oxygen" and "atelactasis" in it.

rpspeck wrote:

I DO NOT, HOWEVER, BELIEVE THAT THE BEST ANSWERS WERE FOUND LAST CENTURY!

I don't mean to imply that they were, but I do think that before assuming NASA does not have good reasons for something you should at least know what their reasons are. The trouble is that you haven’t asked them. Or at least you don’t seem to have done a literature search. Has it been tried before, and if so, what were the results? My experience is that every time I saw a problem that seemed to have an obvious simple solution that was not being used, deeper research into that problem always yielded abundant evidence that the simple solution had been tried, often many times, and did not work for reasons that I was simply not aware of. Now if you had invented some new technology or discovered some new science, that would be different. But you are only using existing technology and science in clearly obvious ways that are not being used by professionals. I just have a hard time believing that the professionals have never tried it before, and if you just asked them, they would tell you why it doesn’t work. For example, Armadillo spent years working on H2O2 engines and differential throttling. The end result is they decided to use gimballed LOX/alcohol engines, just like the major aerospace firms do.

Good advice. On the other hand, I would probably never have found out about the Aviation, Space and Environmental Medicine site if some internet jock called Dr_Keith_H hadn't told me about it!

I agree! I know there are people with answers (such as to my F-22 question), but I don't know how to reach them. The "six degree of seperation" idea suggests each person can reach others who can make the required connection in a few steps. This I am trying to do, and will achieve with your help!

Please note, that the mean free path in a gas decreases as the inverse of increasing molecular density (and thus as the inverse of increasing pressure at fixed temperature). This reduces the diffusion of gasses (probably as the inverse square root of pressure, since the collision frequency increases). If the concentration gradient of a component increases – as a fixed percentage composition – THEN the total diffusion INCREASES with pressure. IF THE CONCENTRATION GRADIENT IS FIXED, as through contact with a biological system (pO2 and pCO2 defined in absolute, not ratio terms with respect to variable pressure), or exchange with a condensed (and fixed concentration) phase, then the total MASS TRANSFER IS REDUCED with increasing total pressure.

I think I have this right. But this also illustrates a problem with applied science and inferences from prior work. The answers, even if correct, depend on exactly what questions were asked. This is also relevant to the later note on H2O2.

We have been using “Mixed Monoprop” H2O2 and Methyl Alcohol much longer than Armadillo, and have obtained very good results. However, we call it an “asymmetrical bipropellant”. We continuously inject a small percentage of concentrated permanganate solution (about 2% to 5%). The ratio is not critical (above a minimum) and this allows easy throttling. What Carmack sought was a fixed, metallic catalyst pack, not the catalyst liquid he knew worked well. Thus, we gain the advantages of this fuel, at the cost of a bit of extra plumbing. He failed to find a solution – WITH THE CONSTRAINTS HE IMPOSED – and has chosen to move onto something else.

We need to go beyond the conclusions reached by previous workers, and see what questions were posed to them, and how those questions were phrased. For example, I have no interest in designing a “luxury spaceliner”, so people can travel to Mars in complete comfort. I will personally accept the demands of high altitude mountaineering (which above 8000 meters usually include wearing a respirator to sleep). A breathing problem which had no reported negative impact on any of the 21 Lunar voyagers, appears to me to be a manageable problem. Few groups climbing Mount Everest escape without some residual effects (at least a bit of frostbite).

Please let me know if any of you succeed in extracting relevant primary research reports from these sources.

and cut-n-paste "oxygen AND atelectasis [ti]" into the search field (this boolean looks for papers which have atelectasis in the title AND oxygen either in the title or in the abstract), this brings up the abstracts/summaries of 135 separate papers, 5 of which are reviews (which is probably what you really want).

If you do this at your local university library, you even get to read whole papers, usually.

rpspeck wrote:

I know there are people with answers (such as to my F-22 question), but I don't know how to reach them. The "six degree of seperation" idea suggests each person can reach others who can make the required connection in a few steps. This I am trying to do, and will achieve with your help!

You can get email addresses very simply through (e.g.) google. I do this all the time when I want to contact people (whom I don't know and never met) about papers they have written which interest me. There is usually enough information in the by-line to track down the requisit contact.

In the developed western world the internet has effectively removed 5 degrees of separation.

I find your interpretations of gas diffusion dynamics very difficult to understand. I find that suspect by itself. Perhaps someone out there will help or back you up?

That was better, but still not perfect. I would need to be in a library where copies of the journal are available since the full reports are not available online. It does seem as though most of the reports are anecdotal cases of pilots returning from flights or short term tests at seal level and not long term controlled experiments under Apollo type conditions.